﻿#region 命名空间

using System;

#endregion

namespace Sharp.Domain
{
    public static class IdentityGenerator
    {
        /// <summary>
        ///     顺序Guid
        /// </summary>
        /// <returns></returns>
        public static Guid NewSecuentialGuid()
        {
            byte[] uid = Guid.NewGuid().ToByteArray();
            byte[] binDate = BitConverter.GetBytes(DateTime.UtcNow.Ticks);

            byte[] secuentialGuid = new byte[uid.Length];

            secuentialGuid[0] = uid[0];
            secuentialGuid[1] = uid[1];
            secuentialGuid[2] = uid[2];
            secuentialGuid[3] = uid[3];
            secuentialGuid[4] = uid[4];
            secuentialGuid[5] = uid[5];
            secuentialGuid[6] = uid[6];
            // set the first part of the 8th byte to '1100' so     
            // later we'll be able to validate it was generated by us   
            secuentialGuid[7] = (byte)(0xc0 | (0xf & uid[7]));
            // the last 8 bytes are sequential,    
            // it minimizes index fragmentation   
            // to a degree as long as there are not a large    
            // number of Secuential-Guids generated per millisecond  
            secuentialGuid[9] = binDate[0];
            secuentialGuid[8] = binDate[1];
            secuentialGuid[15] = binDate[2];
            secuentialGuid[14] = binDate[3];
            secuentialGuid[13] = binDate[4];
            secuentialGuid[12] = binDate[5];
            secuentialGuid[11] = binDate[6];
            secuentialGuid[10] = binDate[7];

            return new Guid(secuentialGuid);
        }

        /// <summary> 
        /// Generate a new <see cref="Guid"/> using the comb algorithm. 
        /// </summary> 
        public static Guid GenerateComb()
        {
            byte[] guidArray = Guid.NewGuid().ToByteArray();

            DateTime baseDate = new DateTime(1900, 1, 1);
            DateTime now = DateTime.Now;

            // Get the days and milliseconds which will be used to build    
            //the byte string    
            TimeSpan days = new TimeSpan(now.Ticks - baseDate.Ticks);
            TimeSpan msecs = now.TimeOfDay;

            // Convert to a byte array        
            // Note that SQL Server is accurate to 1/300th of a    
            // millisecond so we divide by 3.333333    
            byte[] daysArray = BitConverter.GetBytes(days.Days);
            byte[] msecsArray = BitConverter.GetBytes((long)
              (msecs.TotalMilliseconds / 3.333333));

            // Reverse the bytes to match SQL Servers ordering    
            Array.Reverse(daysArray);
            Array.Reverse(msecsArray);

            // Copy the bytes into the guid    
            Array.Copy(daysArray, daysArray.Length - 2, guidArray,
              guidArray.Length - 6, 2);
            Array.Copy(msecsArray, msecsArray.Length - 4, guidArray,
              guidArray.Length - 4, 4);

            return new Guid(guidArray);
        }
    }
}